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We propose a compact computational method based on the capacitance model for the efficient design of graphene-based synaptic field effect transistors (FETs), in which the hysteresis of conduction characteristics due to the channel–gate interface trap is used as synaptic plasticity. Using our method to calculate the conduction properties of graphene and armchair graphene nanoribbon (AGNR) superlattice FETs, it is shown that the AGNR can achieve an efficient conductance change rate Δ w , which is approximately 7.4 times that of graphene. It was also found that Δ w was the greatest when the gate oxide thickness was around 2–3 nm, which is near the limit of miniaturization. These results suggest that the proposed synaptic FETs are a promising approach to realize large scale integration chips for biological timescale computation. [ABSTRACT FROM AUTHOR]

We present a numerical study on the impact of electron–phonon scattering on the performance of a strained-graphene field-effect transistor, where the Dirac point of the channel region is shifted along the transverse momentum direction by a strain-induced vector potential and a high on-current/off-current (I on / I off ) ratio as well as a subthreshold slope (SS) steeper than 60 mV/dec have been predicted in the absence of the electron–phonon interaction previously. By using the Dirac-type effective Hamiltonian description for strained graphene and the non-equilibrium Green's function method to systematically account for the electron–phonon scattering, along with Poisson's equation, we demonstrate that the abovementioned I on / I off ratio and SS value can be maintained even in the presence of electron–phonon scattering, although the I on / I off ratio and the I D range over which the steep SS persists are reduced. [ABSTRACT FROM AUTHOR]

We have investigated the influence of nonparabolicity both of an imaginary band located in a bandgap and of a conduction band to improve the accuracy of energy levels for the design of GaInAs/AlInAs mid-infrared quantum cascade lasers (QCLs). The lasing wavelength of the QCL obtained experimentally was compared to that of the calculated optical gain peak by utilizing the single-band non-equilibrium Green's function (NEGF) method. We calculated the energy-dependent effective mass of electrons used in the NEGF calculation from the complex band structure of each bulk material forming the QCL. In a widely lasing wavelength range of 5–10 μm, the calculated gain peaks of the QCLs each agreed very well with the lasing wavelengths obtained experimentally. We have confirmed that in designing the QCL structures, energy dependency of the energy effective mass in the complex bands is significant. [ABSTRACT FROM AUTHOR]

We study the density of states (DOS) in a cylindrical quantum box formed by a cylindrical penetrable barrier and a planer penetrable double barrier perpendicular to the cylinder. The control of the cylindrical barrier thickness or height is found to cause the dimensional transitions from a three-dimensional (3D) DOS to a quasi-one-dimensional (Q1D) DOS and from a quasi-two-dimensional (Q2D) DOS to a quasi-zero-dimensional (QOD) DOS, if the strength of the planer double barrier is zero and infinity, respectively. In between the 3D and the Q1D (Q2D and QOD) limiting regimes, we found the presence of a Q2D (Q1D) like crossover regime. [ABSTRACT FROM AUTHOR]

We investigate the electrical transport characteristics of graphene channel field-effect transistors (FETs) gated via ionic solid (IS), where the conventional gate insulator, such as SiO 2 , has been replaced by solid electrolytes, such as LiP 3 O 4. In this study, we focus on (i) the gate controllability of the current in comparison to conventional graphene FETs with SiO 2 as an insulating material and (ii) the transient characteristics of the drain current and time required to switch on the current. We employ the tight-binding formalism and Boltzmann equation to calculate the electronic band structure and the electronic transport in graphene, while the Nernst–Planck–Poisson equations have been employed to calculate the time-dependent charge distribution in solid electrolytes and the resulting electric double layer formation at the graphene/IS and IS/gate interfaces. Our simulations have shown that graphene FET gated via IS shows superior gate controllability more than SiO 2 -gated graphene FET with the insulator thickness of 1 nm, and the saturated drain current is insensitive to the IS thickness. Moreover, the time required to switch on the drain current is proportional to the thickness of IS, and the limited number of Li + ion vacancies in IS is preferable in obtaining faster switching than the case of unlimited vacancy cases while keeping the superior gate controllability. [ABSTRACT FROM AUTHOR]

We study computationally the electronic transport properties through mechanically squashed zigzag carbon nanotubes (CNTs) under the uniform electric field perpendicular to the tube axis, based on the tight-binding molecular dynamics method for the structural analysis and the Landauer-Büttiker's formalism for the transport analysis. Our simulations show that the band gaps of the zigzag carbon nanotubes exhibit nonlinear decrease as increasing the deformation ratio in the presence of the external perpendicular electric field, in contrast to the case of zero electric field, where the band gap decreases linearly as increasing the deformation ratio. Such properties allow us to tune the sensitivity of the electromechanical response in CNT devices by applying the external electric field. [ABSTRACT FROM AUTHOR]